Plasma display devices using plasma display panels (PDPs), which have the advantages of being large, thin, and lightweight, are a subject of increasing interest as color display devices for computers and television sets.
A plasma display device additively mixes three primary colors to give a full-color display by means of a phosphor layer that emits light in three primary colors: red (R), green (G), and blue (B). Ultraviolet rays generated in discharge cells of the PDP excite the phosphor particles constituting this phosphor layer such that they emit visible light of each color.
The chemical compounds used in the phosphor of each color mentioned above are (YGd)BO3:Eu3+ and Y2O3:Eu3+ which emit red light, Zn2SiO4:Mn2+ which emits green light, and BaMgAl10O17:Eu2+ which emits blue light. Phosphors are manufactured by mixing predetermined materials, and then firing the mixture at above 1,000 ° C. to induce a solid-phase reaction (refer to Ohmsha's Phosphor Handbook, pp. 219–220). The phosphor particles made by firing are ground and screened (classified). The average particle diameter of red and green phosphors is 2 μm to 5 μm and the average particle diameter of blue phosphor is 3 μm to 10 μm.
Phosphor particles are ground and screened (classified) for the following reasons. Normally, phosphor particles for each color are made into paste and screen-printed, or phosphor ink is dispensed from a thin nozzle using the ink-jet process to form the phosphor layer on the PDP. Accordingly, a smooth layer is achievable by the use of small and uniformly sized phosphor particles (even particle size distribution) when the paste is applied. In other words, a smaller phosphor particle diameter, a more even shape, and closer to that of a sphere achieve a smoother application surface. This improves the packing density of the phosphor particles in the phosphor layer, increases the light-emitting surface of particles, and also minimizes the risk of unstable address driving. As a result, the luminance of the plasma display device can theoretically be improved.
However, in practice, the use of phosphor particles with a smaller diameter increases the surface area of the phosphor and therefore of the risk of defects in the phosphor. This likely to cause more water, carbon dioxide, or hydrocarbon system organics attach to the phosphor surface. In particular, blue phosphor, in which divalent Eu ions in substances such as in Ba(1-x)MgAl10O17:Eux and Ba(1-x-y)SryMgAl10O17:Eux are the luminescence center, has a layer crystal structure (e.g. Display and Imaging 1999, vol. 7, pp. 225–234). In this layer structure, oxygen (O) present near a layer containing a Ba atom (the Ba—O layer) has defects regardless of the particle diameter, and the number of defects increases with falling particle diameter (e.g. Applied Physics, vol. 70, No. 3, 2001, p. 310)
In addition, it is known that ultraviolet rays with wavelength 147 nm generated by discharge when driving the panel also cause defects in the phosphor (e.g.
Technical Report EID 99-94, Jan. 27, 2000, Electronic Information and Communications Society). FIG. 6 is a schematic structure of the Ba—O layer in BaMgAl10O17:Eu blue phosphor.
In a conventional blue phosphor, the occurrence of these defects is believed to cause degradation of luminance. More specifically, defects caused by ions generated when driving the panel that collide with the phosphor, and defects caused by ultraviolet rays of wavelength 147 nm are thought to degrade luminance.